ONTOGENY OF OSMOREGULATORY STRUCTURES IN THE SHRIMP PENAEUS-JAPONICUS(CRUSTACEA, DECAPODA)

The ontogeny of differentiated osmoregulatory epithelia in the branchi al chamber (gills, branchiostegite, pleura, epipodite) was studied by transmission electron microscopy throughout the postembryonic developm ent of Penaeus japonicus. These epithelia are characterized by typical cytological features, including apical microvilli and numerous basal infoldings associated with mitochondria.Differentiated osmoregulatory structures are not observed in the early larval stages: nauplii and zo ea 1. In the next larval stages, zoeas and mysis, gills and epipodites are developed as buds only, but osmoregulatory epithelia are observed in the branchiostegites and pleurae. The differentiated structures of the branchiostegites and pleurae are still present in postlarvae but disappear in juveniles and adults. Gills and epipodites develop progre ssively in the postlarval stages, with early differentiation of osmore gulatory epithelia in the epipodites. In juveniles and adults, the gil l epithelium is poorly differentiated; in contrast, abundant different iated osmoregulatory structures are observed in the epipodites. Ontoge netical comparisons of these observations with previous studies in the same species reveal strong correlations between the development of os moregulatory epithelia, the ability to osmoregulate, the activity of N a+-K+ ATPase, and salinity tolerance during the postembryonic developm ent of Penaeus japonicus.